The invention is related to clutching devices generally and more specifically to an engine driven apparatus for driving at least one vehicle mounted accessory at either one of two selectable speeds.
Planetary gear sets are often used in drive units for speed changing applications by selectively restraining one of either the ring gear, the sun gear or the planet gear carrier. One such drive unit is illustrated in U.S. Pat. No. 2,959,070. In the context of an accessory drive unit for automotive applications the planet gear set may be employed as a means for driving the accessory at a speed that is different from the speed of the engine (crankshaft). Overdriving the accessory, that is, to drive it faster than the speed of the engine reduces the useful life of the gear unit and often generates an unacceptable level of accoustic whine. Further, prior drive units have used planetary gear sets to drive the accessory at only either of two speeds, the first speed being equal to input speed and the second speed differing from the first by the effective gear ratio of the gear set. Further, when driving through the planetary gear set, it is necessary to selectively fix one of its components from rotating to achieve one of the two output speeds. Such means for fixing the rotation of the gear set components include, for example, extentions to the ring gear, planetary carrier or sun gear which engaged by means of a brake, such as a brake caliper, adding size, weight and cost to the accessory drive.
It is an object of the present invention to provide an engine driven, clutched drive capable of driving a belt driven accessory to full speed and reduced speed. A further object is to provide such a device utilizing a speed reducing planetary gear set. An additional object of the present invention is to provide means for performing the clutching function in a simple manner. A further object of the present invention is to provide a self-actuating braking device which automatically affectuates speed changes.
Many other objects and purposes of the invention will become apparent from the detailed description.
Accordingly the invention is directed to a multi-speed accessory drive having a plurality of operating conditions in which an output member is rotated at the speed of an input or driving member or at a reduced speed ratio. The drive comprising a planetary gear set including a sun gear, a plurality of planet gears and a ring gear interconnected with the sun gear, wherein the sun gear is drivingly connected to the input member and the planet gears are drivingly connected to the output member. The drive further includes a driving link rotatably fixed to the input member including spring means fixed to the driving member and to a pressure plate for rotating the pressure plate and for axially urging the pressure plate away from the driving link and clutch means comprising the pressure plate axially movable relative to the input member. The drive additionally includes means for moving the pressure plate into contact with and for rotationally engaging the output member and for alternatively drivingly connecting the output member to the input member; and means for self-disengaging the ring gear during intervals when the pressure plate is in engagement with the output member to permit the output member to rotate at the speed of the input member and for automatically halting the rotation of the ring gear when the pressure plate is disengaged from the output member to permit the output member to rotate at a predetermined ratio of the speed of the input member.